Treatment chambers for the above purposes comprise a closed heat insulating housing having an inlet slot and an exit slot for the flat material web. Slotted nozzles are arranged as nozzle sets and reach into the housing to cause the treatment medium flow to pass crosswise to the feed advance direction of the flat material web. The nozzle sets extend across the width of the material web and several such sets are arranged in a row as viewed in the feed advance direction. The slotted nozzle sets are connected to blower means for supplying and withdrawing the gaseous treatment medium.
It is known to treat flat material webs of thermoplastic synthetic film for improving certain physical characteristics of such films or webs. The treatment is applied immediately following an extrusion, a calendering, or a pouring of the film, whereby suitable treatment equipment is used in treatment chambers for stretching or fixing the flat material web also referred to as film herein.
Another type of treatment of such films involves coating the films with liquid media and subsequently passing the coated films through a drying chamber or chambers.
One heat treatment in a known apparatus involves the passing of a temperature controlled gaseous medium, preferably air, through a plurality of slotted nozzles across the entire width of the material web crosswise to the feed advance direction. The slotted nozzles are arranged as mentioned, in a row as viewed in the feed advance direction and extend across the entire film width either on one or both sides of the film. In order to avoid heat loss as much as possible, the treatment chambers are substantially closed, except for an entrance and an exit for the material web or film. In addition, the treatment chamber or chambers are well heat insulated.
U.S. Pat. No. 4,170,075 discloses a drying chamber as part of a treatment plant, with a blowing nozzle arrangement suitable for treating web or sheet-type flat materials. The blowing nozzles are arranged crosswise to the feed advance direction of the web and in a row as well as above and below the material web. The nozzles reach across the width of the web. These blowing nozzles are supplied with a gaseous medium by at least two blowers which blow into medium distribution channels. One blower is mounted on each side of the drying chamber longitudinal axis on the inner wall of the drying chamber and below the drying chamber bottom. The medium distribution channels include a vertically arranged medium channel section on the inner chamber wall, leading into further distribution channel sections arranged below and above the blowing nozzles and extending at a right angle to the longitudinal blowing nozzle axis. The vertical channel sections and the horizontal channel sections form a channel unit.
In the known apparatus the withdrawal of the gaseous medium from the drying chamber does not take place in a defined manner. As a result, it is possible that the gaseous medium can travel from one drying chamber or cell into another. Such uncontrolled flow or travel of the gaseous medium is undesirable because it results in the application of gaseous drying flows having different temperatures in different areas on the surface of the film to be dried, whereby exposure of the film to different temperatures at different times during its travel through the drying chamber causes surface defects in the film or material web. Such defects are referred to as "schlieren" which in the form of streaks or discolorations make the film unsightly. Another disadvantage of the relatively uncontrolled flow of the drying medium in the conventional apparatus leads to heat losses due to different temperatures in the drying medium circulating circuit. Another conventional disadvantage is seen in that a plurality, at least two, blowers must be used for each drying chamber in order to cause the gaseous drying medium to flow through the channel system to the blowing nozzles and onto the material web or film.